The invention is directed to an arrangement, particularly a heart pacemaker, comprising a measuring means for acquiring a measurement parameter of heart activity.
International Patent Application WO 89/06990 discloses how it is possible to implement a hemodynamic optimization of the frequency control with the assistance of a periodic change of the stimulation frequency, the simultaneous acquisition of a measurement parameter proportional to the cardiac minute output, and appropriate calculating methods. What is critical in this measuring method, however, is that the frequency changes occur over time intervals that not only result in a reaction of the heart muscle, but also result in a reaction of the entire cardiovascular control system; and that this reaction is the prerequisite for desired optimization of the frequency range of the stimulation frequency.
In a heart pacemaker disclosed by EP-A00 255 899, the stimulation frequency is regulated dependent on the atrioventricular transition time as a stress-dependent reference variable input. In addition to characteristics control, a hemodynamic optimum control is thereby also provided in that the stimulation frequency is increased or reduced given a constant degree of physical stress until the measured atrioventricular transition time has a minimum value, whereby the stimulation frequency found in this way is considered optimum for the respective degree of stress. What is also critical in this method is that the frequency changes in the search for the optimum simulation frequency result not only in a reaction of the heart muscle, but of the entire cardiovascular control system as well, whereby this reaction is a prerequisite for the desired optimization of the stimulation frequency.
EP-A-0 140 472 proposes the control of the stimulation frequency dependent on changes of the stroke volume of the heart, whereby these changes are identified with the assistance of impedance measurement. This publication, however, contains no teaching as to how the stroke volume can be quantified with the assistance of the measured values acquired from the impedance signal. It is also not recited how the individual differences of the proportionality between the value of the measured impedance signal and the degree of stress can be compensated.
DE-A-35 33 597 discloses a method wherein the stimulation frequency is regulated with a measured quantity proportional to the stroke volume. The control characteristic of the stimulation frequency as a function of the stroke volume is thereby independently identified in that the frequency is set given maximum stress such that the product of frequency and stroke volume becomes maximum. The disadvantage of this method is that the maximum stress condition must be detected by a second measured parameter, or must be externally input, and that no teaching is provided as to how the susceptibility of the impedance signal to disturbance is compensated, thus the method of this type has not enjoyed practical application.